Small breaking changes and additions
- Closed and Forgiven properties are now nullable on Invoices
- Amount is now nullable on InvoiceItemUpdateOptions to fix a bug where the amount could be set to zero
- StripeError now contains "decline_code"
- added the destination field to StripeChargeCreateOptions
- Transfer.Canceled has been renamed to Transfer.Reversed
- added StripeInvoiceCreateOptions and updated readme